CDROM, short for Compact Disc-Read-Only Memory is a type of optical disk capable of storing large amounts of data -- up to 1GB, although the most common size is 650MB. A single CD-ROM has the storage capacity of 700 floppy disks. CD-ROMs cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. CD-ROM players are also capable of playing audio CDs.